The new deal will keep the 21-year-old, who is currently third choice behind Craig Gordon and Marton Fulop, at the club until 2012.
“We have seen a huge improvement in Trevor in recent months,” Black Cats boss Steve Bruce told the club’s official website.
“He’s still very young in goalkeeping terms, but he’s brave, a good shot-stopper and has excellent distribution.
“He’s relishing working with Nigel Spink and being involved with the first-team and the challenge for Trevor now is to be pushing Craig and Marton for a regular place in the first-team squad.”
